ABSTRACT Hypertension is more prevalent in men than in young women, but as women progress towards menopause this relationship is reversed. Unfortunately, compared to men, menopausal women are less likely to receive optimal diagnostic evaluation and therapeutic intervention. In women, the increased incidence of hypertension begins at ?perimenopause?, a transitional phase preceding and extending through menopause beginning at ~45-54 years of age. The perimenopausal period is accompanied by irregular estrous cycles and erratically fluctuating estrogen levels; it may also be a critical period for the emergence of brain plasticity that may contribute to the development of hypertension. The reversal of hypertension liability in young and older women may be phylogenetically conserved: aged female mice, but not young female mice, show increased sympathetic tone and blood pressure following slow-pressor angiotensin II (AngII) administration. To better understand the role of ovarian hormones in female hypertension, we have utilized a mouse model of accelerated ovarian failure (AOF) that uniquely recapitulates hormone fluctuations seen in human menopause. Using AOF mice, we made the novel finding that the susceptibility to hypertension begins at ?peri-AOF?, which is a stage marked by irregular and extended estrous cycles similar to human perimenopause. In addition, peri-AOF hypertension was associated with a unique profile of N-methyl-D-aspartic acid (NMDA) receptor plasticity in estrogen receptor ? (ER?) containing neurons in the hypothalamic paraventricular nucleus (PVN) not seen in pre- or post-AOF females, or in males. These findings define peri-AOF as a critical period when hypertension and adaptations in neuro-cardiovascular regulatory systems emerge. In the current proposal, we will investigate the role of ER? in the emergence of hypertension and PVN NMDA receptor plasticity during peri-AOF. For this, we will test the central hypothesis that ER? influences the susceptibility to hypertension and NMDA receptor plasticity in select populations of PVN neurons in peri-AOF mice following slow-pressor AngII administration. Two aims will test this hypothesis. Aim 1 will test the sub- hypothesis that ER? in the PVN is critically involved in the susceptibility of peri-AOF females to hypertension and potentiated NMDA receptor-mediated excitatory signaling in CRF-expressing neurons. Aim 2 will test the sub-hypothesis that cyclic administration of ER? agonists during peri-AOF reduces both hypertension susceptibility and NMDA-mediated excitatory signaling selectively in CRF-containing PVN neurons. These studies will be achieved using a multidisciplinary approach including spatio-temporal deletion of the ER? gene, electron microscopic immunocytochemistry, molecular and biochemical assays and neurophysiological methods.